Apparatus and method for sending and receiving free space optical signals
A free space optical communication system incorporates a kinematic sensor, such as an accelerometer, proximate an optical signal generator or emitter, such as a laser. Kinematic information generated using an output signal from the kinematic sensor is encoded along with a time signal and transmitted from the sending node to a receiving node. The receiving node receives the kinematic information and determines a future position and orientation of the sending node. The receiving node makes adjustments to receiving optical component hardware in order to better receive the signal based upon the acceleration data and the time signal.
The instant invention relates generally to free space optical communication systems, and more particularly to laser beam tracking and pointing for free space optical communication systems.
BACKGROUNDA variety of technologies are available for supporting high data rate communication. In applications where it is desired to support very high bandwidth it is common to provide an optical waveguide, also referred to as a fiber optic cable or optical fiber, between a light source and a receiver. Thus, a light source provides a light signal to an optical waveguide and the optical waveguide guides the light signal to the receiver. Unfortunately, in many cases it is not convenient or even feasible to string an optical fiber from one location to another location. In addition, optical waveguides are subject to physical damage.
An alternative communication system uses radio signals to transfer data. A radio communications system is much easier to install than a system that relies upon optical waveguides because typically there is no need for any physical infrastructure between the transmitter and the receiver. Unfortunately, radio communication systems offer lower bandwidth than optical communication systems. In addition, since radio signals typically are not well confined, the transmitted signal is fairly easy to monitor.
In order to provide high bandwidth communication between two locations that are fairly close together it is also known to use free space optics. A free space optical communication system uses typically a laser to emit an optical signal toward a receiver. The optical signal is not confined by an optical waveguide and so it is a requirement that the emitter and the receiver have an unobstructed line of sight therebetween. Free space optical (FSO) systems also have a few inherent drawbacks. For example, any object that is disposed between the signal emitter and the signal receiver will affect the propagation of the optical signals. In addition, the distance between the signal emitter and the receiver is limited to about 2 kilometers using conventional laser-based FSO equipment. Another challenge to using free space optical systems is that it is often difficult to ensure that the separate components are aligned correctly. More specifically, while the components may be properly aligned at one point in time, that alignment is subject to change under normal operating conditions. For example, if a laser-based emitter is disposed on the top of a very high tower then the laser may move slightly in very windy conditions. Alternatively, a train passing nearby may shake the earth beneath the tower enough that the laser is pointing momentarily in a direction that prevents good communications. Similarly, the receiver is also subject to small movements that may reduce signal quality.
The prior art teaches a variety of techniques for minimizing the effects of these types of alignment problems in FSO systems. For example, CANON™ supports a product called “CANOBEAM™” which is a laser signal emitter featuring a system to compensate for small, angular misalignments.
In U.S. Pat. No. 6,347,001 issued to Arnold et al., the entire contents of which is incorporated herein by reference, an error signal indicative of angular misalignment is generated. This signal is provided to an actuator that serves to compensate for the misalignment. The tracking system of Arnold et al. uses an actuated mirror to support both a communications laser and a fine tracking centroider. The actuator for controlling the orientation of the mirror relies upon an error signal that is proportional to an angular difference between the bore sight of the receiving terminal and the line of sight to the opposite transceiver.
The above-mentioned systems and techniques are suitable for their intended purpose of compensating for small, angular misalignments between emitters and sensors that are mounted to stationary structures. Unfortunately, this type of compensation does not allow for the use of FSO communication between mobile platforms, such as for instance moving vehicles, etc.
It would be beneficial to provide a system that supports robust free space optical communication by ensuring that the laser and receiver are properly aligned.
SUMMARY OF EMBODIMENTS OF THE INVENTIONAccording to at least one embodiment of the instant invention, sensor data relating to current kinematic information is provided along with a conventional data transmission between communicating FSO devices. According to at least one embodiment of the instant invention, an accelerometer is integrated into each FSO communication device for measuring the said current kinematic information.
According to an aspect of the instant invention there is provided an apparatus for sending and receiving free space optical signals, comprising: a kinematic information sensor for providing first kinematic data relating to the apparatus at a first known time; a transmitter for launching a first optical signal along a free space optical communications pathway, the first optical signal comprising the first kinematic data; a receiver for sensing a second optical signal, the second optical signal comprising second kinematic data relating to a second apparatus at a second known time; a processor for determining alignment data for aligning the transmitter and the receiver of the first apparatus with a receiver and a transmitter of the second apparatus, respectively, the alignment data being determined based on the first kinematic data and the second kinematic data; and, an actuator in communication with the transmitter and with the receiver, for aligning the transmitter and the receiver in dependence upon the determined alignment data.
According to an aspect of the instant invention there is provided an apparatus for sending and receiving free space optical signals, comprising: an accelerometer for measuring first acceleration data relating to the apparatus; a timer for providing first time data that is indicative of a time of measurement of the first acceleration data; an encoder for providing an encoded signal comprising the first acceleration data and the first time data; an emitter for launching a first optical signal along a free space optical communications pathway, the first optical signal comprising the encoded signal; an optical sensor for sensing a second optical signal that is emitted from a second apparatus, the second apparatus also being an apparatus for sending and receiving free space optical signals; a decoder for extracting from the second optical signal second acceleration data relating to the second apparatus and second time data indicative of a time of measurement of the second acceleration data; a processor for determining alignment data for supporting free space optical communication between the apparatus and the second apparatus at a future time; and, an actuator for adjusting an alignment status of the emitter and of the optical sensor based on the alignment data, wherein the alignment data is determined based on the first acceleration data, the first time data, the second acceleration data and the second time data.
According to an aspect of the instant invention there is provided a method for aligning optical components of a free space optical (FSO) communications system, comprising: determining first kinematic data relating to a first FSO communications device of the FSO communications system at a first known time, using a kinematic sensor that is local to the first FSO communications device; receiving at the first FSO communications device a FSO communications signal transmitted from a second FSO communications device of the FSO communications system, the FSO communications signal comprising second kinematic data relating to the second FSO communications device at a second known time; processing the first kinematic data and the second kinematic data locally with respect to the first FSO communications device, for determining alignment data for supporting communication between the first FSO communications device and the second FSO communications device at a future time; and, aligning the optical components of the first FSO communications device based on the determined alignment data.
According to an aspect of the instant invention there is provided a method for aligning optical components of a free space optical (FSO) communications system, comprising: measuring first kinematic data using a sensor mounted within a first FSO communications device of the FSO communications system; measuring second kinematic data using a sensor mounted within a second FSO communications device of the FSO communications system; providing the first kinematic data to the second FSO communications device; providing the second kinematic data to the first FSO communications device; processing the first kinematic data and the second kinematic data locally with respect to the first FSO communications device for determining first alignment data for supporting communication with the second FSO communications device at a future time; and, processing the first kinematic data and the second kinematic data locally with respect to the second FSO communications device for determining second alignment data for supporting communication with the first FSO communications device at the same future time.
According to an aspect of the instant invention there is provided an apparatus for sending and receiving free space optical signals, comprising: a kinematic sensor for providing first kinematic data relating to the apparatus; a timer for providing first time data that is indicative of a time of measurement of the first kinematic data; a plurality of free space optical communication ports, each one of the plurality of free space optical communication ports comprising: an emitter for launching a first optical signal along a free space optical communications pathway, the first optical signal comprising the first kinematic data and the first time data; an optical sensor for sensing a second optical signal, the second optical signal comprising second kinematic data relating to a second apparatus and comprising second time data that is indicative of the time of measurement of the second kinematic data; a processor in communication with the kinematic sensor for receiving the first kinematic data therefrom and in communication with the timer for receiving the first time data therefrom, the processor for determining alignment data for aligning the emitter and the optical sensor with an optical sensor and an emitter of the second apparatus, respectively, the alignment data being determined based on the first kinematic data and the second kinematic data; and, an actuator in communication with the emitter and with the optical sensor, for aligning the emitter and the optical sensor in dependence upon the determined alignment data; and, a switch for supporting exchange of payload data between different free space optical communication ports of the plurality of free space optical communication ports.
Exemplary embodiments of the invention will now be described in conjunction with the following drawings, in which similar reference numerals designate similar items:
The following description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments disclosed, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
Throughout the detailed description and in the appended claims, the following terms are to be defined as follows. The term “alignment” refers to a relative spatial orientation between the optical components of two FSO devices, which supports communication therebetween via a free space optical communications pathway. The term “aligning” refers to changing the relative spatial orientation between the optical components of two FSO devices in a way that improves or enhances alignment therebetween. It is to be understood that the term “aligning,” when used with reference to only one FSO device or system, means changing the spatial orientation of the one FSO device or system relative to a second other FSO device or system. The term “adjusting an alignment status” means changing the relative spatial orientation between the optical components of two FSO devices from a first relative spatial orientation to a second relative spatial orientation so as to improve or enhance alignment therebetween.
Referring to
A person of skill in the art will appreciate that a variety of optical components are optionally disposed between the laser 101 and the optical sensor 102. These optical components typically are included in order to increase the intensity of the optical signal that is incident upon the optical sensor 102, thereby supporting good communication over longer distances. The disadvantage of providing such components is that the resulting FSO system is often rendered more sensitive to misalignment between the laser 101 and the optical sensor 102.
Referring now to
In order to minimize errors in alignment between the FSO devices, each FSO device 201 and 202 is provided with a kinematic sensor that is suitable for measuring local kinematic information associated with the emitter and optical sensor of the FSO device. There are a variety of sensors that are suitable for measuring kinematic information, such as for instance speed sensors, accelerometers and global positioning system (GPS) receivers, to name but a few non-limiting examples. When both of the FSO devices 201 and 202 share kinematic information therebetween, it becomes possible to generate a prediction of the locations and orientations (i.e. 201a and 202a in
A person of skill in the art of kinematics will appreciate that there are a variety of different kinematic data that are useable for estimating the future location of the FSO devices. For example, in a first case a FSO device includes a six-axis accelerometer and the kinematic information is current acceleration information. In this case it is also necessary to provide an initial condition of displacement and velocity. Alternatively an accelerometer on a first FSO device provides six-axis acceleration information that is processed along with sensed current velocity and sensed position data by the first FSO device to generate a specific future estimated position and orientation thereof. In this case, the kinematic information comprises estimated future position and orientation information relating to the first FSO device. Thus, the receiving FSO device simply decodes the position and orientation information. In yet another case, a first FSO device determines a current position and orientation using an external telemetry signal. The first FSO device includes a six-axis velocity sensor. The current position and orientation information, along with the six-axis velocity information, is then provided to a second FSO device, which estimates a future position and orientation of the first FSO device. A variety of other methods of estimating future position and orientation information may also be envisaged by one of skill in the art.
It is convenient to describe the FSO devices as using a same optical element for emitted and sensed optical signals, even though this may introduce certain complexities into the optical design. That being said, such designs do exist, for example Arnold et al. in U.S. Pat. No. 6,347,001 makes use of a single mirror supporting both an emitter and a sensor. However, for a given FSO device the sensor and the emitter need not be disposed at the same location. Thus, some FSO devices have a sensor that is provided at a different location than the emitter. In this configuration it is expected that the sensor include a first optical element mechanically coupled to a first actuator and that the emitter include a second optical element mechanically coupled to a second actuator.
For many applications, kinematic information conveniently is shared between communicating FSO devices via the FSO communication link itself. However, for some applications this need not be the case. For instance, an airplane and a ground station may use a FSO secure communication link for exchanging secure data therebetween. The position and orientation of the aircraft is not secure information and accordingly this data may be transmitted to the ground station via radio signals. Accordingly, the future position of the aircraft-based FSO relative to the ground-station-based FSO is determined in a straightforward manner, based on the transmitted position and orientation data of the aircraft.
For completeness, it should also be noted that the distance between FSO devices represents very useful information for estimating the future positions and orientations. A person of skill in the art will appreciate that a FSO link is optionally used to send an electromagnetic signal between the FSO devices, and that an accurate measurement of the duration of the signal may then be used to compute the distance between the FSO devices.
Of course, over extended periods of time even small errors in the estimated future positions of the FSO devices may accumulate and lead to a failure to align the FSO devices. There are a variety of prior art techniques available that attempt to overcome this problem. By way of a specific and non-limiting example, the optical sensor is provided as an array of optical sensor elements. When the FSO devices are “ideally” aligned, a central sensor element of the sensor array receives the optical signal. When the FSO devices are only slightly misaligned the optical signal is incident on a sensor element other than the central sensor element. This deviation is optionally used to estimate errors in the present kinematic information, and to compensate for such errors. Clearly, providing a larger number of sensor elements on an optical sensor array supports providing more accurate feedback information and/or compensates for larger errors. This technique is described by Dishman et al. in U.S. Pat. No. 6,181,450, the entire contents of which is incorporate herein by reference, and by Kahn in “Secure Free-Space Optical Communication Between Moving Platforms,” EECS Department, University of California, Berkeley, Calif. 94720 USA. However, larger arrays of sensor elements are expensive and are not robust. By way of another specific and non-limiting example, a first FSO device provides a cone shaped optical signal that is used to scan and determine the location of one or more predetermined targets on a second FSO device. When a target is found, the first FSO device is able to verify the relative position and orientation of the second FSO device.
Referring now to
Optionally, calibration of the FSO communications system is based on precise measurements of propagation delay between two communicating FSO devices, as is shown in
-
- B1−(x1′+Δx, y1′+Δy, z1′+Δz)
- B2−(x2′+Δx, y2′+Δy, z2′+Δz)
- B3−(x3′+Δx, y3′+Δy, z3′+Δz)
where it is assumed that the accumulated error during the three consecutive measurements (at positions B1, B2 and B3) can be ignored. The distances L1, L2 and L3 between device A and device B at times t1, t2 and t3, respectively, are measured accurately. Next, the actual coordinates of B1, B2 and B3 versus device A are determined mathematically based on the estimated coordinates of B1, B2 and B3 as measured using the accelerometer and based on the accurately measured distances L1, L2 and L3. Once the actual coordinates of B1, B2 and B3 are known, it is possible to calibrate the system to a condition in which the instantaneous vector of accumulated error is zero. Advantageously, the feedback method discussed supra is based on precise distance measurements as a reference for correction of estimated coordinates. Application of the method does not require additional components for either of the devices A or B, and does not affect communication bandwidth.
It is also worth mentioning that FSO systems require at least a partially transparent path between an emitter and a sensor thereof. Therefore, it is an expected result that a FSO system will lose the FSO communication signal when the FSO path is blocked, even though the emitter and the sensor are otherwise correctly aligned. There are a variety of techniques available for reestablishing communication between the nodes of an FSO system when the FSO path once again becomes available after being blocked for a period of time. Unfortunately, re-establishing communication between FSO nodes may take some time, thereby delaying the use of the FSO communications link. Clearly, such disruptions are to be avoided. Advantageously, a system according to at least an embodiment of the instant invention is intended to minimize such disruptions. For instance, if the disruption is sufficiently brief it may be possible to estimate the relative location and orientation of the FSO devices based on the last kinematic information that was exchanged therebetween prior to the disturbance. That being said, it will be apparent to one of skill in the art that such a system is intended primarily for maintaining an FSO link once it has already been established. Thus, the FSO devices should also support systems and methods for establishing communications between devices that are not already in communication. Such systems and methods are known in the art, such as for example as described by Kahn.
Referring now to
Referring still to
The first FSO device 300 also includes a receiver portion including an optical sensor 303, such as for instance a photodiode, for receiving an optical signal comprising encoded frame data propagating along a free space optical communications path 320b. The sensor 303 is operatively coupled to the actuator 302, which adjusts the sensor 303 in dependence upon the estimated position and orientation of the second FSO device 310 relative to the first FSO device 300. A signal comprising the encoded frame data is provided from the sensor 303 to a decoder 306, which extracts the frame header data and the frame payload data. The frame header data is provided to the processor 307, whilst the frame payload data is provided to an external device via a not illustrated data port.
The actuator 302 optionally adjusts the emitter 301 and the sensor 303 either together or independently of one another. In one embodiment, the actuator 302 includes a first actuator for adjusting the emitter 301, and a second actuator for adjusting independently the sensor 303. By way of a specific and non-limiting example, the emitter 301 includes a laser and an optical element such as for instance a reflective optical element (i.e. a mirror). The optical element is in optical communication with the laser for receiving a free space optical communication signal from the laser and for controllably directing the free space optical communication signal along a predetermined free space optical communications pathway. To this end, the first actuator is mechanically coupled to the optical element for controllably adjusting the optical element relative to the laser, such that an optical signal provided from the laser travels to the optical element and is directed thereby along the predetermined free space optical communications pathway. Similarly, the sensor 303 includes a photodiode and an optical element such as for instance a reflective optical element (i.e. a mirror). The optical element is in optical communication with the photodiode for receiving a free space optical communication signal from another FSO communication device and for controllably directing the free space optical communications signal to the photodiode. To this end, the second actuator is mechanically coupled to the optical element for controllably adjusting the optical element relative to the photodiode. Of course, it will be apparent that alternative optical designs that are suitable for alternative embodiment of the instant invention may feature, for instance, transmissive optical elements.
The second FSO device 310 is substantially identical to the first FSO device. The second FSO device 310 includes a transmitter portion including an emitter 319, such as for instance a laser, for launching an optical signal along the free space optical communications path 320b. A high-precision positioning device, hereinafter referred to simply as actuator 311, is operatively coupled to the emitter 319 for controllably adjusting the emitter 319 in dependence upon a predicted position and orientation of the first FSO device 300 relative to the second FSO device 310. A kinematic information sensor, such as for instance accelerometer 314, is mounted proximate the emitter 319. The accelerometer 314 provides acceleration information to a processor 315, which in turn provides the acceleration information to an encoder 318. A timer/timestamp generator 321 provides a time value to the processor 315, which in turn provides the time value to the encoder 318. The encoder 318 combines the acceleration information with the time value to provide an output frame header. A not illustrated data port supports communication between the encoder 318 and an external device (not shown). When the external device provides external data via the data port, the external data is parsed to provide a frame payload comprising payload data. When payload data is not available a null frame payload is provided. The encoder 318 combines the frame header and the frame payload to provide a frame. A signal comprising encoded frame data is provided from the encoder 318 to the emitter 319, which launches a FSO signal comprising the encoded frame data along the free space optical communications path 320b.
The second FSO device 310 also includes a receiver portion including an optical sensor 312, such as for instance a photodiode, for receiving an optical signal comprising encoded frame data propagating along the free space optical communications path 320a. The sensor 312 is operatively coupled to the actuator 311, which adjusts the sensor 312 in dependence upon the predicted position and orientation of the first FSO device 300 relative to the second FSO device 310. A signal comprising the encoded frame data is provided from the sensor 312 to a decoder 317, which extracts the frame header data and the frame payload data. The frame header data is provided to the processor 315, whilst the frame payload data is provided to an external device via a not illustrated data port.
The actuator 311 optionally adjusts the emitter 319 and the sensor 312 either together or independently of one another. In one embodiment, the actuator 311 includes a first actuator for adjusting the emitter 319, and a second actuator for adjusting independently the sensor 312. By way of a specific and non-limiting example, the emitter 319 includes a laser and an optical element such as for instance a reflective optical element (i.e. a mirror). The optical element is in optical communication with the laser for receiving a free space optical communication signal from the laser and for controllably directing the free space optical communication signal along a predetermined free space optical communications pathway. To this end, the first actuator is mechanically coupled to the optical element for controllably adjusting the optical element relative to the laser, such that an optical signal provided from the laser travels to the optical element and is directed thereby along the predetermined free space optical communications pathway. Similarly, the sensor 312 includes a photodiode and an optical element such as for instance a reflective optical element (i.e. a mirror). The optical element is in optical communication with the photodiode for receiving a free space optical communication signal from another communication device and for controllably directing the free space optical communications signal to the photodiode. To this end, the second actuator is mechanically coupled to the optical element for controllably adjusting the optical element relative to the photodiode. Of course, it will be apparent that alternative optical designs that are suitable for alternative embodiment of the instant invention may feature, for instance, transmissive optical elements.
In order to ensure reliable communication between FSO devices it is desirable to obtain the most accurate estimation possible of the future position and orientation of the FSO devices, one relative to the other. The accuracy of such an estimate is typically higher when the estimate is made into the very near future, and when the current position and orientation information are highly accurate. The further out in time the estimate is projected, the less accurate it is likely to be. For this reason, the FSO devices 300 and 310 each measure current kinematic information relating thereto at regular intervals Δtk. The FSO devices 300 and 310 subsequently exchange the current kinematic information therebetween. Based on current kinematic information relating to both of the FSO devices 300 and 310, each processor 307 and 315 calculates the coordinates of both FSO devices 300 and 310 at a future time. For instance, processor 307 calculates the expected position of emitter 301 between time tk and time tk+1, at regular intervals of time Δts, where Δts is the interval of time between sending frames and where Δts<<Δtk. In other words, processor 307 determines the approximate expected position of emitter 301 at the various times that frame data are transmitted therefrom, for an interval of time between two successive kinematic information measurements. In addition, the same processor 307 also calculates the coordinates of the sensor 312 of the second FSO device 310 between time tk+Δtp and time tk+1+Δtp, at regular intervals of time Δts, where the propagation delay Δtp is the time that is required for an optical signal to travel between the first FSO device and the second FSO device. In other words, processor 307 also determines the expected approximate position of sensor 312 at the various times that frame data are received thereat, for an interval of time between two successive kinematic information measurements. Furthermore, processor 307 calculates the expected position of the sensor 303, and of the emitter 319 of the second FSO device 310.
In an analogous manner, processor 315 determines the expected approximate position of emitter 319 at the various times that frame data are transmitted therefrom, and determines the expected approximate position of sensor 303 at the various times that frame data are received thereat. Furthermore, the processor 315 also determines the expected approximate position of the sensor 312, and of the emitter 301 of the first FSO device 300. Of course, since the optical signal requires a finite amount of time Δtp to propagate between two points in space, the emitter of one FSO device is not aimed precisely at the estimated location of the optical sensor of the other FSO device at the time the optical signal is launched. Rather, the emitter is aimed at a point in space that the optical sensor of the other FSO device is expected to occupy at a time Δtp after the optical signal is launched.
It should also be noted that the timers 308 and 321 of the two FSO devices 300 and 310 are synchronized one with the other. Accordingly, each FSO device estimates the relative position and orientation of the other FSO device at a same future time between tk and tk+1 relative to synchronized timestamp values, which timestamp values are exchanged between the communicating FSO devices along with the current kinematic information. Accordingly, each FSO device performs the estimation independently, based on kinematic information that is measured locally using an accelerometer of that FSO device at a time tk as determined using a timer that is also local to that FSO device, as well as based on kinematic information that is measured using an accelerometer that is local to the other FSO device at a time tk as determined using a timer that is also local to the other FSO device.
It is often desirable to produce an FSO network in the form of a grid or mesh. Such network topologies rely upon nodes that support a relatively large number of optical paths. Such a node supports point to multi-point communication. Referring to
Referring now to
In use, the accelerometer 902 measures acceleration information relating to the FSO node 900 in a manner that is analogous to that which was described supra with reference to
The switch 906 supports payload data exchange between the different FSO ports 908a-c. For instance, when a second FSO node is in communication with FSO node 900 via FSO port 908a and a third FSO node is in communication with FSO node 900 via FSO port 908b, then payload data that is received from the second FSO node is passed via the switch 906 from FSO port 908a to FSO port 908b to be transmitted to the third FSO node. In this way, the second FSO node communicates indirectly with the third FSO node via FSO node 900.
Of course, a person of skill in the art will appreciate that in some cases a FSO node according to the embodiment of the invention as described with reference to
Optionally, the data frame described with reference to
When the actuators are sufficiently responsive and the kinematic information is received in a timely fashion, an FSO system described with reference to
A person of skill in the art will appreciate that an FSO system according to an embodiment of the instant invention is suitable for mounting to structures. More specifically, conventional FSO components are ideally mounted to very stable structures, which helps to ensure that the optical beams are always pointed in the correct direction. In some cases, FSO systems for structures are designed to compensate for small movements. Using a system according to an embodiment of the instant invention, it is clear that a structure that sways in the wind or experiences vibration due to, for example, nearby trains is still suitable as an FSO mounting location. Similarly, an FSO system according to an embodiment of the instant invention is optionally deployed on the hook of a crane, etc. In this way, the operator of the crane can see exactly where the crane payload is positioned. Optionally, an FSO system according to an embodiment of the instant invention is deployed on a surface vehicle such as for instance a sailing ship, a tank, or an armored personnel carrier for supporting FSO communications with other surface vehicles, aircraft, ground stations or satellites. Further optionally, an FSO system according to an embodiment of the instant invention is deployed on an aircraft or satellite, for supporting FSO communications with other aircraft, satellites, surface vehicles or ground stations.
In addition, a system according to an embodiment of the instant invention may be deployed on underwater vehicles, such as for instance manned or unmanned submarine vessels. This is a particularly advantageous application, since radio frequency signals do not propagate through water, and accordingly communications between underwater vehicles is problematic. By way of a specific and non-limiting example, FSO communication signals that are transmitted from a surface craft are able to propagate through the water to an unmanned submarine vessel, for controlling the movements and actions of the said unmanned submarine vessel. Alternatively, the high bandwidth capability of the FSO communications devices makes it practical to consider other novel applications, such as for instance a mechanically decoupled periscope. In this latter case, one or more periscope devices may be deployed by an underwater vehicle, or by another vessel that is either in the air or on the water surface. Once FSO communication is established between the underwater vehicle and the periscope device, images that are captured by the periscope device may be transmitted securely to the underwater vehicle. Furthermore, provided the periscope device includes a propulsion system, the underwater vehicle may control the periscope device remotely, so as to change the direction of viewing, zoom in or out, etc. Advantageously, the underwater vehicle may be positioned at a safe depth and location away from the periscope device, whist still being able to selectably view the activity that is occurring above the surface of the water.
Numerous other embodiments of the invention will be apparent to one of skill in the art without departing from the spirit or scope of the invention. Specifically, there are a variety of other configurations of an FSO system that will easily achieve analogous functionality without using exactly the same hardware configuration. For example, the processor is described as supporting a variety of different data transfer and computing operations. Clearly, the different tasks optionally are carried out by different processors. Similarly, some of these tasks are well suited to be performed by an application specific integrated circuit (ASIC) or programmable logic controller (PLC) that acts as a processor.
Claims
1. An apparatus for sending and receiving free space optical signals, comprising: wherein the alignment data is determined based on the first acceleration data, the first time data, the second acceleration data and the second time data.
- an accelerometer for measuring first acceleration data relating to the apparatus;
- a timer for providing first time data that is indicative of a time of measurement of the first acceleration data;
- a data input port for receiving external data from a first external source;
- an encoder in communication with the accelerometer, the timer and the data input port, the encoder configured for providing an encoded signal comprising the first acceleration data, the first time data, and first payload data, the first payload data based on the external data;
- an emitter for launching a first optical signal along a free space optical communications pathway, the first optical signal comprising the encoded signal;
- an optical sensor for sensing a second optical signal that is emitted from a second apparatus, the second apparatus also being an apparatus for sending and receiving free space optical signals;
- a decoder for extracting from the second optical signal second acceleration data relating to the second apparatus, second time data indicative of a time of measurement of the second acceleration data, and second payload data, the second payload data provided to the second apparatus from a second external source;
- a processor for determining alignment data for supporting free space optical communication between the apparatus and the second apparatus at a future time; and,
- an actuator for adjusting an alignment status of the emitter and of the optical sensor based on the alignment data,
2. An apparatus according to claim 1, wherein the actuator comprises a first actuator for adjusting the alignment status of the emitter and a second actuator for adjusting separately the alignment status of the optical sensor.
3. An apparatus according to claim 2, wherein the emitter comprises:
- a laser; and,
- a first optical element for receiving the first optical signal from the laser and for controllably directing the first optical signal along the free space optical communications pathway.
4. An apparatus according to claim 3, wherein the first actuator is mechanically coupled to the first optical element for controllably adjusting an angle between the first optical element and the laser in dependence upon the alignment data.
5. An apparatus according to claim 2, wherein the optical sensor comprises:
- a light detector; and,
- a second optical element for receiving the second optical signal and for controllably directing the second optical signal toward the light detector.
6. An apparatus according to claim 5, wherein the second actuator is mechanically coupled to the second optical element for controllably adjusting an angle between the second optical element and the light detector in dependence upon the alignment data.
7. An apparatus according to claim 1, comprising a data output port in communication with the decoder, the data output port for providing the second payload data from the decoder to the first external source.
8. A method for aligning optical components of a free space optical (FSO) communications system, comprising:
- measuring first kinematic data using a sensor mounted within a first FSO communications device of the FSO communications system;
- measuring second kinematic data using a sensor mounted within a second FSO communications device of the FSO communications system;
- providing the first kinematic data to the second FSO communications device via a previously established FSO communications link;
- providing the second kinematic data to the first FSO communications device via the previously established FSO communications link;
- processing the first kinematic data and the second kinematic data locally with respect to the first FSO communications device for determining first alignment data for supporting communication with the second FSO communications device at a future time;
- processing the first kinematic data and the second kinematic data locally with respect to the second FSO communications device for determining second alignment data for supporting communication with the first FSO communications device at the same future time; and,
- based on the first alignment data and the second alignment data, adjusting an alignment status of the FSO communications system.
9. A method according to claim 8, wherein adjusting the alignment status of the FSO communications system comprises aligning optical components of the first FSO communications device based on the first alignment data.
10. A method according to claim 8, wherein adjusting the alignment status of the FSO communications system comprises aligning optical components of the second FSO communications device based on the second alignment data.
11. A method according to claim 9, wherein aligning optical components of the first FSO communications device comprises aligning an emitter and an optical sensor of the first FSO communications device with an optical sensor and an emitter of the second FSO communications device, respectively.
12. A method according to claim 10, wherein aligning optical components of the second FSO communications device comprises aligning an emitter and an optical sensor of the second FSO communications device with an optical sensor and an emitter of the first FSO communications device, respectively.
13. A method according to claim 8, wherein providing the first kinematic data to the second FSO communications device comprises launching a first FSO communications signal from the first FSO communications device to the second FSO communications device via the previously established FSO communications link, the first FSO communications signal having encoded thereon the first kinematic data and first time data that is indicative of a time of measurement of the first kinematic data.
14. A method according to claim 8, wherein providing the second kinematic data to the first FSO communications device comprises launching a second FSO communications signal from the second FSO communications device to the first FSO communications device via the previously established FSO communications link, the second FSO communications signal having encoded thereon the second kinematic data and second time data that is indicative of a time of measurement of the second kinematic data.
15. A method according to claim 8, wherein the sensor mounted within the first FSO communications device comprises a first accelerometer, and wherein measuring first kinematic data relating to the first FSO communications device comprises measuring first acceleration data relating to the first FSO communications device.
16. A method according to claim 8, wherein the sensor mounted within the second FSO communications device comprises a second accelerometer, and wherein measuring second kinematic data relating to the second FSO communications device comprises measuring second acceleration data relating to the second FSO communications device.
17. An apparatus according to claim 1, wherein the emitter is configured to propagate the first optical signal through water and the optical sensor is configured to sense the second optical signal after propagation through water.
18. A method according to claim 13, wherein launching the first FSO communications signal from the first FSO communications device to the second FSO communications device comprises propagating the first FSO communications signal along a path through water between the first FSO communications device and the second FSO communications device.
19. A method according to claim 14, wherein launching the second FSO communications signal from the second FSO communications device to the first FSO communications device comprises propagating the second FSO communications signal along a path through water between the first FSO communications device and the second FSO communications device.
3989942 | November 2, 1976 | Waddoups |
4995101 | February 19, 1991 | Titterton et al. |
5790291 | August 4, 1998 | Britz |
6181450 | January 30, 2001 | Dishman et al. |
6271953 | August 7, 2001 | Dishman et al. |
6347001 | February 12, 2002 | Arnold et al. |
6570692 | May 27, 2003 | Doucet et al. |
6792185 | September 14, 2004 | Ahrens et al. |
6915080 | July 5, 2005 | Heminger et al. |
6967754 | November 22, 2005 | Bratt et al. |
6970651 | November 29, 2005 | Schuster et al. |
7212706 | May 1, 2007 | White et al. |
7343099 | March 11, 2008 | Wirth et al. |
7424225 | September 9, 2008 | Elliott |
7991294 | August 2, 2011 | Dreischer et al. |
20030035178 | February 20, 2003 | Seaver |
20040151504 | August 5, 2004 | Triebes et al. |
WO 03016959 | February 2003 | WO |
- Kahn, Secure Free-Space Optical Communication Between Moving Platforms, Lasers and Electro-Optics Society, 2002, LEOS 2002, The 15th Annual Meeting of the IEEE, Publication Date: Nov. 10-14, 2002, vol. 2, on pp. 455-456 vol. 2.
Type: Grant
Filed: Apr 8, 2008
Date of Patent: Apr 10, 2012
Patent Publication Number: 20090252499
Assignee: Igor Melamed (Ontario)
Inventor: Naftali Rotgaizer (Ness Ziona)
Primary Examiner: Danny Leung
Attorney: Morris & Kamlay LLP
Application Number: 12/099,711
International Classification: H04B 10/00 (20060101);